1. Technical Field
The present invention relates to a power control apparatus for controlling power supply from a power source to one or more electronic control units.
2. Background Art
An electronic control system is typically provided with electronic control units that are connected with one another through a communication line. Each electronic control unit includes a processing unit in many cases. Each electronic control unit serves to control the drive of an actuator connected thereto in accordance with operation states of operation switches that are connected to own and/or another control unit.
With recent trend of multi-functionalization of an electronic control system, a remarkable increase has been noted in the number of operation switches connected to the control system. Thus, the multi-functional control system is required to quickly detect operation states of a large number of operation switches for control of actuators. So each electronic control unit of the system carries out processing for the detection of operation states at a high clock rate, resulting in increased power consumption.
To suppress the increased power consumption, various countermeasures have been taken in the multi-functional control system. For instance, during the time where no operation switches are operated so that no actuator control is necessary, the electronic control units of the system are changed from an ordinary mode into a wait mode in which processing units of the control units operate at low clock rates or into a halt mode in which the clock remains stopped.
In order to allow electronic control units to change into the halt mode, however, each control unit requires an additional special circuit for measuring whether control unit may change from the ordinary mode or the wait mode into the halt mode or not, resulting in a high-priced electronic control system.
Furthermore, power consumption in the electronic control unit cannot be made zero even in the halt mode. This is because, even if the control system is in an inoperative state as a result of changing into the halt mode, the control system must be restored to an operative state when any one of operation switches is operated. Therefore, the electronic control unit is required to detect pieces of operation information on the operation switches even in the halt mode, yielding a slight power consumption for the detection of information.
As for an electronic control system for passenger car, electronic control units of the system may change into the halt mode for reduction in power consumption, e.g., in a case where a car is parked for a long time or transported to a remote place. However, the electronic control units are arranged to detect, e.g., an operation of an engine start switch in the halt mode, thus yielding a slight power consumption. A slight but continual power supply from an automotive battery to the electronic control units may cause an overdischarge of the battery.
To obviate battery overdischarge during the transportation, a power wire linking the battery and the electronic control units may be detached by manual work from the battery or the control units. However, this requires much labor. In addition, electrification failures and short-circuit failures may be caused during the manual work for wire detachment.